The present invention relates to controlling or varing the welding during high frequency, longitudinal seam welding of tubes and pipes.
The art of the tube and pipe making includes, as a particular process step, the longitudinal seam welding of adjoining or abutting edges of a suitably bent skelp. As a preparatory step it is known to trim the edges and to shape them in a cutting stage so that the edge corners have right angles to the adjoining flat surface portion of the skelp; accordingly, the abutting and adjoining edges of the folded skelp to be welded together, meet at least most plain parallelly to each other. Consequently, a heat transfer barrier is locally set up, and due to the physics underlying the flow and distribution of the electric welding current in the skelp edge zone an excessive amount of heating occurs in the inner and outer corner portions of the edges. They will therefore, fuse slightly earlier than more central edge zone and unfortunately impede a complete removal of the oxide from these more central edge zone portions.